SPECIAL SEMINAR

Friday, November 6, 2009, 10am | Room 3-370

"DNS-based Modelling of Convective Heat Transfer
in Two-Phase Flow with and without Phase-change"

Dr. Djamel Lakehal
ASCOMP GmbH & ETH
Zurich, Switzerland

ABSTRACT

In practical multi-phase flow applications (e.g. in microfluidics or thermal-hydraulics of nuclear reactors), convective heat transfer involves phenomena acting at different time/length scales. At each level of the scale cascade, the flow physics is amenable to numerical prediction by scale-specific strategies; an example of which is interfacial heat & mass transfer. In the first part of the seminar, we shall discuss the results of thorough DNS investigations of interfacial sheared gas/steam-water flows. Selected results of near-interface turbulent transport will be presented, including a rigorous assessment of the Surface Renewal Theory, and a new calibration of the Surface Divergence Model for interfacial heat transfer. More recent data obtained for a condensing steam-water flow will then be presented, including a derived model based on combining 1D analytical derivation and DNS. The model is then applied to a pressurized thermal shock (PTS) problem, using coarse-grained level-set simulations and LES for turbulence.

The second part of the talk will relate to the simulation of heat removal from micro-pipes (1mm) using two-phase flow dynamics. We’ll show the impact of changing the flow regime (bubbly, slug) on the heat transfer rate. The Nusselt number is found to increase up to five folds as compared to equivalent water flow. Here, too, the study has led to the development of a new heat transfer correlations accounting for the bubble/slug local Reynolds number. It is found that the passage of individual inclusions in the pipe play the same role as turbulent eddies in re-washing the fluid-wall surface, i.e. by reference to the Surface Renewal Theory discussed in the first part. We’ll close the seminar by discussing new routes towards modelling liquid film and nucleate boiling.

BIO SKETCH

Dr. Djamel Lakehal is a part-time Lecturer at ETH Zurich (convective heat transfer), and General Manager of ASCOMP GmbH. He obtained a Master degree in Computational Fluid Dynamics & Transport Phenomena from Ecole Centrale of Nantes, France in 1991, and a PhD in December 1994. In the period 1995-1997, he collaborated with Prof. W. Rodi at the University of Karlsruhe as a post-doctoral researcher (turbulence modelling group). As a Research Associate at the Institute of Fluid Mechanics at the TU-Berlin (1997-1998), he collaborated with Prof. F. Thiele on studying vortex-shedding flows past bluff bodies. In 1998, he joined the Institute of Energy Technology of ETH Zurich as a Group Leader and Senior Lecturer, working with Prof. G. Yadigaroglu’s Thermal-hydraulics group, where he initiated the creation of the Computational Multifluid Dynamics Group (CMFG). In November 2004, he defended his ‘Habilitation’ jointly at ETH and Ecole Centrale of Lyon, France. In 2004, together with former members of the CMFG, he founded ASCOMP GmbH; an ETH Spin-off Company specialized in industrial multi-fluids dynamics and heat transfer. Dr. Lakehal collaborates with the Los Alamos National Laboratory; the University of Melbourne; UC Santa Barbara; KTH Stockholm, and FZD Rossendorf in Germany.